The present invention relates to an optomechanical scanning apparatus for an electrostatic copying machine.
Until recently, electrostatic copying machines were designed for either general purpose copying or copying original documents in sheet form. The general purpose machines comprise a glass platen which can support a sheet, book or other original document placed face down thereon. An optical system focusses a light image of the original document onto a photoconductive drum or the like to form an electrostatic image through localized photoconduction. The electrostatic image is developed by means of a toner substance to form a toner image which is transferred and fixed to a copy sheet to provide a permanent reproduction of the original document.
The general purpose machines further comprise a reciprocating system for scanning the document. Either the optical system or the platen is moved relative to the drum to scan the document. Since only the forward portion of the reciprocation is used for scanning, the return portion of the reciprocation constitutes wasted time.
The type of copying machine for sheets only increases the copying speed by eliminating the return portion of the reciprocation. This is accomplished by maintaining the platen and optical system stationary and feeding the original document relative to the drum. The sheet feed may be automated since the sheets are fed in only one direction. The obvious disadvantage of this type of machine is that it can not be used for original documents such as books.
To overcome these drawbacks, combination machines have been developed recently which combine scanning systems for both bulky and sheet documents into a single machine. In one type, both a platen and sheet feed mechanism are provided as an integral unit and are movable relative to a fixed optical system for copying bulky documents. This type of machine has the disadvantage that a large drive motor is required to move the heavy sheet feed mechanism in addition to the platen, thereby adding to the size and cost of the machine to a disproportionate extent.
To overcome the drawback of this type of combination copying machine, another type has been developed in which the platen and sheet feed mechanism are held stationary and the optical system is movable for copying bulky documents. This type of machine suffers from the disadvantage of all copying machines comprising movable optical systems in that the optical systems are complicated and expensive to manufacture and difficult to maintain in alignment.